Context: Good sleep is an important recovery method for prevention
and treatment of overtraining in sport practice. Whether sleep is
regulated by melatonin after red-light irradiation in athletes is
unknown.

Objective: To determine the effect of red light on sleep quality
and endurance performance of Chinese female basketball players.

Design: Cohort study.

Setting: Athletic training facility of the Chinese People's
Liberation Army and research laboratory of the China Institute of Sport
Science.

Patients or Other Participants: Twenty athletes of the Chinese
People's Liberation Army team (age = 18.60 [+ or -] 3.60 years)
took part in the study. Participants were divided into redlight
treatment (n = 10) and placebo (n = 10) groups.

Intervention(s): The red-light treatment participants received 30
minutes of irradiation from a red-light therapy instrument every night
for 14 days. The placebo group did not receive light illumination.

Main Outcome Measure(s): The Pittsburgh Sleep Quality Index (PSQI)
questionnaire was completed, serum melatonin was assessed, and 12-minute
run was performed at preintervention (baseline) and postintervention (14
days).

Conclusions: Our study confirmed the effectiveness of body
irradiation with red light in improving the quality of sleep of elite
female basketball players and offered a nonpharmacologic and noninvasive
therapy to prevent sleep disorders after training.

Good sleep is a prerequisite for optimal performance. (1) Given
that people spend about one-third of their lives asleep, sleep has
substantial functions for development, daily functioning, and health.
(2) Perhaps no daytime behavior has been associated more closely with
improved sleep than exercise. (3) Researchers have shown that exercise
serves as a positive function for sleep. Regular exercise consistently
has been associated with better sleep. (4) Moreover, the American
Academy of Sleep Medicine considers physical exercise to be a modality
of nonpharmacologic treatment for sleep disorders. (4) When studying the
influence of exercise on sleep, most investigators have compared acute
exercise and sedentary control treatments. (5) In their study of chronic
moderate-intensity endurance exercise, Driver and Taylor (6) also
provided compelling evidence that exercise promotes sleep.

However, exercise can negatively affect sleep quality. Exercising
immediately before going to sleep is detrimental to sleep quality. (7)
Athletes train very hard to improve their on-field performances, but
excessive training may lead to a decrease in performance, which is known
as overtraining syndrome. Researchers (8) have shown that symptoms of
overtraining indicate poor-quality sleep. Good sleep is an important
recovery method for prevention and treatment of overtraining in sport
practice. (9)

Evidence is compelling that chronic exposure to bright light (3000
lux) can enhance sleep. (10) Guilleminault et al (11) suggested that the
effects of exposure to light may be more powerful than those associated
with exercise. In a recent study in which red-light therapy (wavelength
= 670 nm, light dose = 4 J/[cm.sup.2]) was used, Yeager et al (12)
indicated that red light could restore glutathione redox balance upon
toxicologic insult and enhance both cytochrome c oxidase and energy
production, all of which may be affected by melatonin. Melatonin is a
neurohormone that is produced by the pineal gland and regulates sleep
and circadian functions. (13) No one knows whether sleep is regulated by
melatonin after red-light irradiation in athletes. Researchers (14,15)
have demonstrated that phototherapy improves muscle regeneration after
exercise. Red light could protect human erythrocytes in preserved
diluted whole blood from the damage caused by experimental artificial
heart-lung machines. (16) However, the effect of red-light illumination
on endurance performance is a new topic in sport science.

Sleep quality can be defined subjectively by self-report (17) or by
more objective measures, such as polysomnography or actigraphy. (18)
Subjective sleep quality has been assessed most widely with the
Pittsburgh Sleep Quality Index (PSQI). (17) The PSQI is a comprehensive
18-item self-report questionnaire assessing sleep disturbances in the
previous month. It derives ordinal scores for 7 clinically relevant
domains of sleep: subjective sleep quality, sleep latency, sleep
duration, habitual sleep efficiency, sleep disturbances (eg, awakenings
from sleep due to discomfort, bad dreams), use of sleeping medication,
and daytime dysfunction (feeling sleepy during the day due to a poor
night's sleep). Scores from these separate components are combined
to derive a global measure of sleep quality. (19)

As demonstrated in these studies, acute or chronic exercise may
lead to good- or bad-quality sleep. However, the effects of red light on
sleep quality and endurance performance have not been investigated
sufficiently. Therefore, the purpose of our study was to determine the
effect of red light on the sleep quality and endurance performance of
Chinese female basketball players.

METHODS

Participants

Twenty female athletes of the Chinese People's Liberation Army
team (age = 18.60 [+ or -] 3.60 years) participated in the study.
Participant characteristics are described in Table 1. All participants
were healthy and were not using medications regularly or temporarily
during the measurements. Athletes were excluded if they had participated
in less than 80% of the scheduled team physical training and basketball
sessions for the last 3 months or used any kind of nutritional
supplements or pharmacologic agents. All participants provided written
informed consent, and the study was approved by the Ethical Committee of
the China Institute of Sport Science.

Design

We used a randomized parallel pretest-posttest design. Participants
were assigned randomly to either a red-light therapy intervention group
(n = 10) or non-red-light therapy intervention group (placebo group, n =
10). Measurements were collected at preintervention (baseline) and
postintervention (14 days). The exercise training schedule of the 2
groups was unchanged during the 14 days; the red-light treatment group
used a red-light therapy instrument every night for total body
irradiation for 30 minutes. The training routine of the athletes during
the 14 intervention days included 12 exercise sessions with the
following specifications: 2 hours of morning training, 2 hours of
afternoon training, and no training on Sunday.

[FIGURE 1 OMITTED]

The red-light treatment participants lay in the supine position,
and continuous illumination was performed using noncoherent red light
from a whole-body red-light treatment machine (Shanghai Dayou PDT
Technology Co, Ltd, Shanghai, China) with an average wavelength of 658
nm and light dose of 30 J/[cm.sup.2]. The whole body received the
phototherapy treatment (Figure 1). In general studies, investigators
have used 14 days (20,21) or 7 days (22) as 1 session period, so we
chose 14 days as a trial time. The placebo participants also lay in the
supine position under the red-light device but did not receive any light
illumination. All participants wore swimsuits to enhance irradiation
from the device and were blind to the treatment.

Measurement

Sleep Quality. Sleep quality was measured by the Chinese version of
the PSQI. (17) The 19-item measure assesses sleep quality and
disturbances over a half-month time interval. The total PSQI score
ranges from 0 to 21, and higher scores reflect poorer-quality sleep.
(17) The 7 items of this instrument measure several aspects of insomnia:
difficulties with onset and maintenance of sleep, satisfaction with the
current sleep pattern, interference with daily functioning, noticeable
impairment attributed to sleep problems, degree of distress, and concern
caused by any sleeping problems.

Cooper 12-Minute Run. Participants were instructed to complete as
many laps as possible on a 400-m outdoor track during the 12-minute test
period. Emphasis was placed on pacing oneself throughout the test. The
test administrators (J.Z., D.L., and J.X.) counted the laps completed
during the 12-minute test period while calling out the time elapsed at
3, 6, and 9 minutes and orally encouraging the participants. At the end
of the 12-minute period, the test administrator instructed the
participants to stop and used a measuring wheel to determine the
fraction of the last lap completed by each participant. This distance
was added to the distance determined by the number of laps completed to
give the total distance covered during the test.

[FIGURE 2 OMITTED]

Serum Melatonin. In humans, the serum level of melatonin, which is
derived mainly from the pineal gland, demonstrates a clear increase at
night and a decrease during the day. (23,24) Given that the masking
effects of activities (eg, exercise, sleep, and food intake (25,26))
have little effect on the daily pattern of the circulating melatonin
level, melatonin secretion appears to directly reflect the function of
the biological clock as a specific marker of circadian rhythm. (27) We
drew blood samples in the morning (8:00 AM) of preintervention and
postintervention. Melatonin in the serum was measured in pictograms per
milliliter using an enzyme-linked immunosorbent assay kit (Melatonin
ELISA; IBL, Hamburg, Germany).

Statistical Analysis

Data were analyzed using descriptive statistics, 2-way analyses of
variance (ANOVAs), and t tests for independent means. Isolated
comparisons between groups (experimental, control) and times
(preintervention, postintervention) were performed only in cases where
time x group interactions were found. We used Pearson product moment
correlation coefficients to determine the relationships among sleep
quality, serum melatonin, and endurance performance. The [alpha] level
was set at .05. We used SPSS (version 16.0; IBM Corporation, Armonk, NY)
for data analysis.

RESULTS

Participants

We found no differences in any of the baseline characteristics
between the groups.

Sleep Quality

We found an effect for group ([F.sub.1,18] = 5.62, P = .03) and a
time x group interaction for global PSQI scores ([F.sub.1,18] = 5.66, P
= .03; Figure 2). At preintervention, we found no difference between the
groups ([t.sub.18] = -0.53, P = .60). At postintervention, participants
in the red-light treatment group demonstrated greater improvement in
global PSQI scores than the placebo group ([t.sub.18] = -4.55, P <
.001). Descriptive statistics and statistical values for the PSQI
subscores are listed in Table 2. Among the subscores, we found a time x
group interaction for subjective sleep quality ([F.sub.1,18] = 6.70, P =
.02) and effects of group for sleep duration ([F.sub.1,18] = 5.36, P =
.03) and sleep latency ([F.sub.1,18] = 5.65, P = .03). We noted an
effect of time for daytime dysfunction ([F.sub.1,18] = 6.40, P = .02).
We did not observe an effect of group or a time x group interaction for
habitual sleep efficiency ([F.sub.1,18] = 2.49, P = .13 and [F.sub.1,18]
= 2.84, P = .11, respectively) or sleep disturbance ([F.sub.1,18] =
0.21, P = .65 and [F.sub.1,18] = 3.32, P = .09, respectively) variables.

We noted an effect of time for distance ([F.sub.1,18] = 12.76, P =
.004). We observed a trend toward improvement but no time x group
interaction ([F.sub.1,18] = 1.72, P = .22). A difference was found
between preintervention and postintervention of the red-light treatment
group ([t.sub.18] = 3.54, P = .005; Figure 4).

We demonstrated a correlation between changes in global PSQI and
serum melatonin levels (r = -0.695, P = .006; Table 3). We also saw a
trend toward a negative relationship between change in global PSQI and
distance of the 12-minute run test at preintervention and
postintervention for all participants (r = -0.353, P = .07; Table 3). In
addition, when the results of the postintervention were analyzed alone,
we found a negative correlation between change in the distance of the
12-minute run test and global PSQI (r = -0.579, P = .02).

DISCUSSION

Our results indicated that a 14-day program of red-light treatment
improved sleep and serum melatonin levels. Although the statistical
analysis did not reveal differences between groups for running distance
in the aerobic exercise test, the percentage increase in the red-light
treatment group (12.8%) was higher than the percentage increase in the
control group (5.5%; P < .05).

[FIGURE 4 OMITTED]

The PSQI revealed that the improvements in global PSQI scores and
sleep quality were greater at postintervention in the red-light
treatment group than in the placebo group. In addition, we found an
effect of time for daytime dysfunction ([F.sub.1,8] = 6.40, P = .02).
Sack et al (28) suggested a role of melatonin in facilitating sleepiness
during the night by inhibiting a central nervous system
wakefulness-generating system. The positive effect seen m our study may
be due to relatively higher melatonin levels after the red-light
illumination. Our results are in accordance with those reported in
previous studies, showing that melatonin might be a principal component
of red-light therapy. (12) In their analysis of the effects of light on
melatonin levels and rhythms in humans, Wright and Lack (29) showed
that, whereas shorter wavelengths of blue (430 nm) and green (540 nm)
light suppress salivary melatonin and shift the melatonin rhythm, red
light (610 nm and 660 nm) has no effect on melatonin suppression and
slightly shortens the time before dim-light onset of melatonin
secretion. Recently, Figueiro and Rea (22) demonstrated that blue light
reduced nocturnal levels of melatonin, whereas red light increased them.
However, our observations contradicted those reported in studies of
adults with insomnia in which researchers (30) reported negative
relationships between the red-light condition and improved sleep
variables and daytime symptoms. Conflicting results in the literature
may stem from studying different participants. In our study, the
participants were female basketball players who did not have severe
insomnia.

We observed an effect of time on distance ([F.sub.1,8] = 12.76, P =
.004), such that 12-minute run distance was longer after 14 days of
red-light illumination in basketball players. For the 12-minute run
distance, an effect was noted for time but not for group; no time x
group interaction was seen. Therefore, we could not draw a clear
conclusion that redlight illumination induced positive changes in
endurance performance among basketball players. With regard to the
association of red light and exercise, the data are quite scarce. As far
as we know, only 1 study (31) of red light and exercise in human
participants has been published. The study was carried out in healthy,
physically active male volunteers, and treatment with light-emitting
diodes produced a smaller decrease in maximal isometric torque after
high-intensity concentric isokinetic exercise. Ihsan (32) demonstrated
that laser promoted arteriolar vasodilation and improved the peripheral
microcirculation. In addition, phototherapy could improve the muscle
regeneration after exercise. (33) Therefore, observations by us and by
Baroni et al (31) may be mainly related to increased arteriolar
vasodilation and peripheral microcirculation after red-light
illumination.

We found a correlation between changes in global PSQI and serum
melatonin levels (r = -0.695, P = .006). A negative relationship existed
between decreases in sleep quality and improvements in endurance
performance as determined by 12-minute run distance, but this was only a
trend (r = -0.353, P = .07). We also demonstrated a correlation between
sleep quality and distance of the 12-minute run test during the
postintervention period. This in part may be due to sleep providing
recovery from autonomic reactivity, psychoemotional tension, and
hormonal responses. (34) These results suggest that endurance
performance was mediated by mechanisms other than sleep quality alone.

CONCLUSIONS

We have demonstrated that red-light illumination positively
affected sleep quality and endurance performance variables in Chinese
female basketball players. Based on previous studies, (6,12,14,15,33) we
can infer that red-light treatment contributes to increased melatonin
secretion in the pineal gland and muscle regeneration. To our knowledge,
we are the first to demonstrate the positive effects of red-light
treatment on sleep and aerobic performance, which is an interesting link
with practical application to sports training. Although more studies
involving phototherapy, sleep, and exercise performance need to be
performed, red-light treatment is a possible nonpharmacologic and
noninvasive therapy to prevent sleep disorders after training.

* Red-light illumination is a positive nonpharmacologic and
noninvasive therapy to prevent sleep disorders after training.

doi: 10.4085/1062-6050-47.6.08

ACKNOWLEDGMENTS

This research project was supported by National Key Technologies
R&D Program Fund of China (2006BAK37B06).

We thank Professor Craig G. Crandall for editing and Dr James
Pearson for proofreading the manuscript. We also thank Bin Fan and
Qingde Shi for analyzing and entering the data; Baoxin Feng, Peifang
Zong, Wenyuan Shang, Weiying Zhang, and Pengfei Li for their technical
assistance; and our volunteers for their willingness to participate in
this project.